[PATCH 5.10 307/406] USB: core: Fix race by not overwriting udev->descriptor in hub_port_init()

Greg Kroah-Hartman
2023-09-17T19:38:36Z

From: Alan Stern <stern@rowland.harvard.edu>

commit ff33299ec8bb80cdcc073ad9c506bd79bb2ed20b upstream.

Syzbot reported an out-of-bounds read in sysfs.c:read_descriptors():

BUG: KASAN: slab-out-of-bounds in read_descriptors+0x263/0x280 drivers/usb/core/sysfs.c:883
Read of size 8 at addr ffff88801e78b8c8 by task udevd/5011

CPU: 0 PID: 5011 Comm: udevd Not tainted 6.4.0-rc6-syzkaller-00195-g40f71e7cd3c6 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:351
print_report mm/kasan/report.c:462 [inline]
kasan_report+0x11c/0x130 mm/kasan/report.c:572
read_descriptors+0x263/0x280 drivers/usb/core/sysfs.c:883
...
Allocated by task 758:
...
__do_kmalloc_node mm/slab_common.c:966 [inline]
__kmalloc+0x5e/0x190 mm/slab_common.c:979
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:680 [inline]
usb_get_configuration+0x1f7/0x5170 drivers/usb/core/config.c:887
usb_enumerate_device drivers/usb/core/hub.c:2407 [inline]
usb_new_device+0x12b0/0x19d0 drivers/usb/core/hub.c:2545

As analyzed by Khazhy Kumykov, the cause of this bug is a race between
read_descriptors() and hub_port_init(): The first routine uses a field
in udev->descriptor, not expecting it to change, while the second
overwrites it.

Prior to commit 45bf39f8df7f ("USB: core: Don't hold device lock while
reading the "descriptors" sysfs file") this race couldn't occur,
because the routines were mutually exclusive thanks to the device
locking. Removing that locking from read_descriptors() exposed it to
the race.

The best way to fix the bug is to keep hub_port_init() from changing
udev->descriptor once udev has been initialized and registered.
Drivers expect the descriptors stored in the kernel to be immutable;
we should not undermine this expectation. In fact, this change should
have been made long ago.

So now hub_port_init() will take an additional argument, specifying a
buffer in which to store the device descriptor it reads. (If udev has
not yet been initialized, the buffer pointer will be NULL and then
hub_port_init() will store the device descriptor in udev as before.)
This eliminates the data race responsible for the out-of-bounds read.

The changes to hub_port_init() appear more extensive than they really
are, because of indentation changes resulting from an attempt to avoid
writing to other parts of the usb_device structure after it has been
initialized. Similar changes should be made to the code that reads
the BOS descriptor, but that can be handled in a separate patch later
on. This patch is sufficient to fix the bug found by syzbot.

Reported-and-tested-by: syzbot+18996170f8096c6174d0@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-usb/000000000000c0ffe505fe86c9ca@google.com/#r
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Khazhy Kumykov <khazhy@google.com>
Fixes: 45bf39f8df7f ("USB: core: Don't hold device lock while reading the "descriptors" sysfs file")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/b958b47a-9a46-4c22-a9f9-e42e42c31251@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/core/hub.c | 114 ++++++++++++++++++++++++++++++-------------------
1 file changed, 70 insertions(+), 44 deletions(-)

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4669,10 +4669,17 @@ static int get_bMaxPacketSize0(struct us
* the port lock. For a newly detected device that is not accessible
* through any global pointers, it's not necessary to lock the device,
* but it is still necessary to lock the port.
+ *
+ * For a newly detected device, @dev_descr must be NULL. The device
+ * descriptor retrieved from the device will then be stored in
+ * @udev->descriptor. For an already existing device, @dev_descr
+ * must be non-NULL. The device descriptor will be stored there,
+ * not in @udev->descriptor, because descriptors for registered
+ * devices are meant to be immutable.
*/
static int
hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
- int retry_counter)
+ int retry_counter, struct usb_device_descriptor *dev_descr)
{
struct usb_device *hdev = hub->hdev;
struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
@@ -4684,6 +4691,7 @@ hub_port_init(struct usb_hub *hub, struc
int devnum = udev->devnum;
const char *driver_name;
bool do_new_scheme;
+ const bool initial = !dev_descr;
int maxp0;
struct usb_device_descriptor *buf, *descr;

@@ -4722,32 +4730,34 @@ hub_port_init(struct usb_hub *hub, struc
}
oldspeed = udev->speed;

- /* USB 2.0 section 5.5.3 talks about ep0 maxpacket ...
- * it's fixed size except for full speed devices.
- * For Wireless USB devices, ep0 max packet is always 512 (tho
- * reported as 0xff in the device descriptor). WUSB1.0[4.8.1].
- */
- switch (udev->speed) {
- case USB_SPEED_SUPER_PLUS:
- case USB_SPEED_SUPER:
- case USB_SPEED_WIRELESS: /* fixed at 512 */
- udev->ep0.desc.wMaxPacketSize = cpu_to_le16(512);
- break;
- case USB_SPEED_HIGH: /* fixed at 64 */
- udev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
- break;
- case USB_SPEED_FULL: /* 8, 16, 32, or 64 */
- /* to determine the ep0 maxpacket size, try to read
- * the device descriptor to get bMaxPacketSize0 and
- * then correct our initial guess.
+ if (initial) {
+ /* USB 2.0 section 5.5.3 talks about ep0 maxpacket ...
+ * it's fixed size except for full speed devices.
+ * For Wireless USB devices, ep0 max packet is always 512 (tho
+ * reported as 0xff in the device descriptor). WUSB1.0[4.8.1].
*/
- udev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
- break;
- case USB_SPEED_LOW: /* fixed at 8 */
- udev->ep0.desc.wMaxPacketSize = cpu_to_le16(8);
- break;
- default:
- goto fail;
+ switch (udev->speed) {
+ case USB_SPEED_SUPER_PLUS:
+ case USB_SPEED_SUPER:
+ case USB_SPEED_WIRELESS: /* fixed at 512 */
+ udev->ep0.desc.wMaxPacketSize = cpu_to_le16(512);
+ break;
+ case USB_SPEED_HIGH: /* fixed at 64 */
+ udev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
+ break;
+ case USB_SPEED_FULL: /* 8, 16, 32, or 64 */
+ /* to determine the ep0 maxpacket size, try to read
+ * the device descriptor to get bMaxPacketSize0 and
+ * then correct our initial guess.
+ */
+ udev->ep0.desc.wMaxPacketSize = cpu_to_le16(64);
+ break;
+ case USB_SPEED_LOW: /* fixed at 8 */
+ udev->ep0.desc.wMaxPacketSize = cpu_to_le16(8);
+ break;
+ default:
+ goto fail;
+ }
}

if (udev->speed == USB_SPEED_WIRELESS)
@@ -4770,22 +4780,24 @@ hub_port_init(struct usb_hub *hub, struc
if (udev->speed < USB_SPEED_SUPER)
dev_info(&udev->dev,
"%s %s USB device number %d using %s\n",
- (udev->config) ? "reset" : "new", speed,
+ (initial ? "new" : "reset"), speed,
devnum, driver_name);

- /* Set up TT records, if needed */
- if (hdev->tt) {
- udev->tt = hdev->tt;
- udev->ttport = hdev->ttport;
- } else if (udev->speed != USB_SPEED_HIGH
- && hdev->speed == USB_SPEED_HIGH) {
- if (!hub->tt.hub) {
- dev_err(&udev->dev, "parent hub has no TT\n");
- retval = -EINVAL;
- goto fail;
+ if (initial) {
+ /* Set up TT records, if needed */
+ if (hdev->tt) {
+ udev->tt = hdev->tt;
+ udev->ttport = hdev->ttport;
+ } else if (udev->speed != USB_SPEED_HIGH
+ && hdev->speed == USB_SPEED_HIGH) {
+ if (!hub->tt.hub) {
+ dev_err(&udev->dev, "parent hub has no TT\n");
+ retval = -EINVAL;
+ goto fail;
+ }
+ udev->tt = &hub->tt;
+ udev->ttport = port1;
}
- udev->tt = &hub->tt;
- udev->ttport = port1;
}

/* Why interleave GET_DESCRIPTOR and SET_ADDRESS this way?
@@ -4814,6 +4826,12 @@ hub_port_init(struct usb_hub *hub, struc

maxp0 = get_bMaxPacketSize0(udev, buf,
GET_DESCRIPTOR_BUFSIZE, retries == 0);
+ if (maxp0 > 0 && !initial &&
+ maxp0 != udev->descriptor.bMaxPacketSize0) {
+ dev_err(&udev->dev, "device reset changed ep0 maxpacket size!\n");
+ retval = -ENODEV;
+ goto fail;
+ }

retval = hub_port_reset(hub, port1, udev, delay, false);
if (retval < 0) /* error or disconnect */
@@ -4883,6 +4901,12 @@ hub_port_init(struct usb_hub *hub, struc
} else {
u32 delay;

+ if (!initial && maxp0 != udev->descriptor.bMaxPacketSize0) {
+ dev_err(&udev->dev, "device reset changed ep0 maxpacket size!\n");
+ retval = -ENODEV;
+ goto fail;
+ }
+
delay = udev->parent->hub_delay;
udev->hub_delay = min_t(u32, delay,
USB_TP_TRANSMISSION_DELAY_MAX);
@@ -4926,7 +4950,10 @@ hub_port_init(struct usb_hub *hub, struc
retval);
goto fail;
}
- udev->descriptor = *descr;
+ if (initial)
+ udev->descriptor = *descr;
+ else
+ *dev_descr = *descr;
kfree(descr);

/*
@@ -5229,7 +5256,7 @@ static void hub_port_connect(struct usb_
}

/* reset (non-USB 3.0 devices) and get descriptor */
- status = hub_port_init(hub, udev, port1, i);
+ status = hub_port_init(hub, udev, port1, i, NULL);
if (status < 0)
goto loop;

@@ -5845,7 +5872,7 @@ static int usb_reset_and_verify_device(s
struct usb_device *parent_hdev = udev->parent;
struct usb_hub *parent_hub;
struct usb_hcd *hcd = bus_to_hcd(udev->bus);
- struct usb_device_descriptor descriptor = udev->descriptor;
+ struct usb_device_descriptor descriptor;
struct usb_host_bos *bos;
int i, j, ret = 0;
int port1 = udev->portnum;
@@ -5887,7 +5914,7 @@ static int usb_reset_and_verify_device(s
/* ep0 maxpacket size may change; let the HCD know about it.
* Other endpoints will be handled by re-enumeration. */
usb_ep0_reinit(udev);
- ret = hub_port_init(parent_hub, udev, port1, i);
+ ret = hub_port_init(parent_hub, udev, port1, i, &descriptor);
if (ret >= 0 || ret == -ENOTCONN || ret == -ENODEV)
break;
}
@@ -5899,7 +5926,6 @@ static int usb_reset_and_verify_device(s
/* Device might have changed firmware (DFU or similar) */
if (descriptors_changed(udev, &descriptor, bos)) {
dev_info(&udev->dev, "device firmware changed\n");
- udev->descriptor = descriptor; /* for disconnect() calls */
goto re_enumerate;
}